Abstract. Thin coastal dykes typically found in developing countries may suddenly collapse due to rapid land subsidence, material ageing, sea-level rise, high wave attack, earthquakes, landslides, or a collision with vessels. Such a failure could trigger dam-break tsunami-type flooding, or “dyke-break-induced tsunami”, a possibility which has so far been overlooked in the field of coastal disaster science and management. To analyse the potential consequences of one such flooding event caused by a dyke failure, a hydrodynamic model was constructed based on the authors' field surveys of a vulnerable coastal location in Jakarta, Indonesia. In a 2m land subsidence scenario – which is expected to take place in the study area after only about 10–20 years – the model results show that the floodwaters rapidly rise to a height of nearly 3m, resembling the flooding pattern of earthquake-induced tsunamis. The depth–velocity product criterion suggests that many of the narrow pedestrian paths behind the dyke could experience strong flows, which are far greater than the safe limits that would allow pedestrian evacuation. A couple of alternative scenarios were also considered to investigate how such flood impacts could be mitigated by creating a mangrove belt in front of the dyke as an additional safety measure. The dyke-break-induced tsunamis, which in many areas are far more likely than regular earthquake tsunamis, cannot be overlooked and thus should be considered in disaster management and urban planning along the coasts of many developing countries.

Thin coastal dykes found in developing countries may suddenly collapse due to land subsidence, material ageing, earthquakes, a collision with vessels, etc. Such a failure could trigger a dyke-break-induced tsunami. To analyse the potential consequences of such a flooding event, a hydrodynamic model was created using the data from the authors' field surveys of a vulnerable coastal community in Jakarta. The countermeasure of using mangrove forest is also proposed to mitigate violent floods.

Thin coastal dykes found in developing countries may suddenly collapse due to land subsidence,...